Many type of installation or appliance use water. For example, a shower or sink in a domestic or institutional setting, may use hot and cold water from supplies. The hot and cold water may be mixed by a simple mixing tap, or mixed by a special valve such as a thermostatic mixing valve or TMV. A TMV works by blending hot and cold water from their respective supply pipes to generate water at a preset temperature safe for use by humans. This preset temperature is invariably at a temperature that supports the rapid growth of bacteria. Chemical treatment regimes are sometimes favoured to kill the bacteria, but suitable chemicals tend to be powerful oxidisers, and can cause serious damage to brass components and elastomeric seals. They are also hazardous (e.g. toxic and/or corrosive) in their concentrated form, and therefore dangerous to transport and handle. Moreover, some organisms are resistant to chemicals. One reason for this may be that, where the organisms form a biofilm, for example, dead cells killed by the chemical agent can act as a shield for living layers beneath.
Heat is a reliable method of killing such bacteria, but that initially would appear to be an inappropriate method of killing bacteria in a TMV because the purpose of the TMV is to prevent scalding, and thus the valve never gets to the temperatures that would kill the bacteria.
This apparent conflict has previously been addressed in installations using electronically-controlled solenoid valves. The electronic controller sometimes has a “sterilise option” whereby solenoid valves controlling the water pathways are switched into a position such that the hot supply is internally fed around an appliance in such a way as to heat up the whole appliance. The outlet is then operated and flushes through with unblended hot water. This quickly heats up the whole product to hot water temperature, which should be sufficient to kill any bacteria present within around 5 minutes. However, it also carries the attendant risk of scalding to anyone who happens to be using the facility being sterilised at the time. It is therefore convention to do this at a time when no-one is likely to be using the facility, e.g. overnight. This activity may be initiated/activated by a control computer remote from the individual valves being sterilised, such as a BMS (Building Management System). An electronic thermal sterilising kit is available from Schell GmbH & Co. KG (Armaturentechnologie) of Olpe, Germany. See http://www.schell-armaturen.de/index.php?vw type=artikel&vw id=4431&struktur=1&praesenz=1 and the associated installation instructions that can be downloaded from there. Unfortunately, there is always the risk that one of the solenoid valves could jam, or leak, and that hot water could continue to flow into the cold water inlet of the product, creating a scald risk. There is also the risk that an electronic fault in the controller, or wiring, could permit the sterilise function to operate at an inappropriate time. The mere presence of this remotely operated capability represents a risk. The reliance on electronics also increases the skills required for installation and maintenance.
As an alternative solution, the present applicant has offered a Thermal Disinfection Kit for some valves. The Thermal Disinfection Kit comprises adaptors which fit into the strainer caps of the shower valve, and a hose to cross connect the supplies. In order to do this safely, it is necessary to first isolate the cold water supply, and keep it isolated during the disinfection procedure, which involves opening the Hot Water isolation valve, and then operating the outlet. Failure to do this properly in the correct sequence could result in the mixing valve not being sterilised properly, and also in hot water passing into the cold supply pipework. Fitting the current Thermal Disinfection Kit is inconvenient, requiring several steps, and handling of hot components. These drawbacks are tolerated as it is the only way that the desired outcome can be accomplished. On the other hand, many installations in general use are simply not properly disinfected because of the inconvenience and complexity of the process.